How to assign uvmap to a material
To assign the second material to the second UV map:
1: In Edit mode, UV Editor, enable UV Sync Selection.
2: Box select all the UV vertices at the lower left hand corner.
In the 3D Viewport all the vertices associated with the second UV map should now be selected.
4: Select the second material and Assign this selected geometry.
5: Change the Viewport shading to Material Preview.
When done don't forget to disable the Sync Selection option in the UV Editor.